This invention relates to a high voltage fuse and, more particularly, to a fuse core having a fuse element wrapped about it and constructed to provide increased creepage between adjacent turns of the fuse element and also to provide improved performance of the high voltage fuse.
High voltage fuses conventionally comprise a fusible element embedded in a granular inert material of high dielectric strength such as sand or finely divided quartz. The fusible element may be in the form of a ribbon type silver material which is wound on a supporting core. When subjected to currents of fault magnitude, the fusible element attains a fusing temperature and vaporizes, whereby arcing occurs and the metal vapors rapidly expand to many times the volume originally occupied by the fusible element. The metal vapors are thrown into spaces between the granules of the inert filler material where they condense and are no longer available for current conduction. The current limiting effect results from the introduction of arc resistance into the circuit. The physical contact between the hot arc and the relatively cool granules causes a rapid transfer of heat from the arc to the granules, thereby dissipating most of the arc energy with very little pressure built up within the fuse enclosure.
The core may be provided with angularly-spaced raised fins extending longitudinally of the core along its outer surfaces. The fuse elements having the form of a plurality of silver wires or ribbon may be wrapped in a helical manner along the fins. Such various type cores are described in U.S. Pat. Nos. 3,243,552; 3,294,936 and 3,437,971, issued to H. W. Mikulecky, Mar. 29, 1966, Dec. 27, 1966 and Apr. 8, 1969, respectively. In these patents the fins are provided with cutouts which have the effect of improving insulation between the adjacent turns of the fuse elements. In the fuses shown in these patents, the cutouts are generally large in relation to the fuse element width, and this, as well as other dimensional relationships, makes it generally necessary to use different core designs for different element numbers and/or winding angles.
The aforesaid U.S. Pat. Nos. 3,243,552; 3,294,936; and 3,437,971 also describe a supporting core of insulating material positioned in contact with the fusible element that is adapted to evolve a gas in the presence of an arc. The gas evolving material provides a de-ionizing action that reduces the occurrence of restriking, that is, the occurrence of fuse conduction after the interruption of the transient overload current. The core typically has a high thermal conductivity characteristic that conducts heat away from the fuse element during an overcurrent condition. The cooling effect of the core reduces the available heat to melt the fuse element and thereby reduces the consistency of performance of the high voltage fuse.
Accordingly, an object of my invention is to provide a core which is capable of accommodating fuse elements with various winding angles and in various numbers and yet which always has between adjacent turns the increased creepage distance provided by at least one cutout.
A further object of my invention is to reduce the cooling effect of the supporting core and correspondingly improve the consistency of performance of the high voltage fuse.
These and other objects of the present invention will become apparent to those skilled in the art upon consideration of the following description of the invention.